The invention relates to a method for the manufacture of an elastic twisted yarn whereby at least one outer yarn is wound or twisted around an expanded, elastic core yarn, and in a first process step the outer yarn is wound or twisted around the core yarn at a winding speed providing less than the nominal twist of the finished twisted yarn. The thus formed in-between yarn is wound up and the in-between yarn is twisted in a second process step in the same direction of rotation in order to obtain the desired nominal twist for the finished twisted yarn.
DE 1 173 367 describes a method for the manufacture of yarns in which in a first method step the individual threads are doubled or folded, and are pretwisted with a small twist of up to 3% of the nominal twist. In this manner pretwisted threads are subsequently subjected in a second method step to a further twisting on a bell spindle, whereby the nominal twist is achieved. The first method step is preferably carried out on a ring doubling frame, whereas the high twist in the second method step can, for example, be carried out on a double-twist frame.
It is disadvantageous in this method that the spindle speed is limited to approximately 40 m/s by the rotor speed of the ring spinning frame being used since, as is known, a blocking or rather seizing between the ring and rotor occurs at higher rotor speeds. Higher spindle speeds are thus not possible with the described method.
In addition, conventional twisting machines are known which are also sold under the name Uptwister. Such a twisting machine is, for example, described in the EP 0 078 753 A2. Higher speeds can here basically indeed be achieved due to the missing ring. However, the unwinding speed is limited also in these classic twisting machines, namely because at high spindle speeds the small mass (weight of yarn per meter) of the fine yarns is not sufficient in order to overcome the co-rotating air-limit layer on the surface of the spool. The yarn does not come loose from the spool and a thread balloon is also not formed. This, however, is necessary for an Uptwister process. The centrifugal force of the yarn could indeed be increased with a further increase of the spindle speed, however, as soon as the yarn breaks through the co-rotating air-limit layer and then hits with a high peripheral speed the stationary surrounding air, it is destroyed or at least damaged to the degree that it no longer meets the requirements in the finished product.
Furthermore an extremely high spindle speed on Uptwister twisting machines is not economical because of the high energy consumption.
Furthermore it has in practice been proven to be disadvantageous in the described methods that this behavior also occurs at very low spindle speeds. The air-limit layer does lose its effect, however, the centrifugal force is reduced significantly because of the low speed and the yarn comes no longer loose from the spool. Therefore, when determining the optimum production speed in an Uptwister with a free thread balloon, one has only a very limited margin.
However, an increase of the speed could not be considered since, on the one hand, the energy consumption of a yarn twisting spindle increases significantly with an increasing speed and quickly reaches a range which is no longer economical and, on the other hand, because of the above-disclosed reasons, the thread balloon is incorrectly constructed due to turbulence. As is described in the DE 1 104 653, the energy consumption during twisting depends essentially on the size of the yarn pot and from its speed. The drive power increases approximately with the third power of the speed, with the fourth power of the pot diameter, whereas only approximately with the first power of the pot height. Almost the entire drive power is hereby converted into kinetic energy of the air surrounding the pot, which air at the high speeds of the spinning top of approximately 10,000 rotations/min. and more has a turbulent movement, and therefore creates a high friction. The mentioned reference suggests therefore to provide for the purpose of lowering the energy consumption between the rotating twist chamber and the yarn pot a not driven intermediate housing, which completely or partially surrounds the pot, and which is supported in the spinning chamber or on the drive motor of the pot and is spaced from the wall of the spinning chamber and also from the spinning pot at a distance which is small in relationship to the diameter.
Therefore, the basic purpose exists to provide a two-step method for the manufacture of an elastic twisted yarn so that it is suited also for very fine yarns but can still be driven very economically.
The invention relates to a method for the manufacture of an elastic twisted yarn, whereby at least one outer yarn is wound or twisted around an expanded, elastic core yarn and in a first process step the outer yarn is wound around the core yarn at a winding speed providing less than the nominal or finished twist of the finished twisted yarn, the thus formed intermediate yarn is wound up, and the in-between yarn is twisted in the same direction of rotation in a second process step. In the first process step the outer yarn is twisted with the help of a double-pot spindle and at a winding rate of above 50% of the nominal twist without a balloon forming around the core yarn, and the second process step is carried out on a double-twist spindle.